It is sometimes necessary to sample a signal parameter (for example, the coding complexity) of each of a plurality of data signals. If all the data signals are mutually synchronized, this involves simply providing measuring apparatus, responsive to the data signals, for producing respective signals representing the signal parameter of the data signals, and sampling these parameter representative signals at the appropriate times. However, in cases where the data signals are not in synchronism, but it is desired to control the processing of all of the data signals based on the relative values of the respective signal parameters, it is necessary that the signal parameters be sampled substantially simultaneously in all of the data signals. In this case, the sampling of the signal parameters is a problem.
In an exemplary system, a plurality of video signals from respective channels, which may be television network feeds, television stations, or other video sources, are transmitted over a satellite link for broadcast to respective television receivers in consumers' homes. Each video signal may be encoded into a signal consisting of sequential groups of data, each group including data representing a fixed number of successive video pictures or frames, designated a group of pictures (GOP). While each group in all of the data signals has the same fixed, predetermined time duration (equal to the duration of the number of video pictures or frames in the group), the timing of the groups within the different video signals are not synchronized.
In such a system, data from the different channels is combined, or multiplexed, at a head end station into a single data stream. The multiplexed data stream is then transmitted over a transmission link, such as a wire, fiber optic or radio link (such as the satellite link), to a back end station, where the channels of data from the multiplexed data stream are then separated, or demultiplexed, and supplied to the intended recipients. An exemplary satellite link includes a digital transmission path capable of transmitting 24 megabits per second (Mbps). In order to maximize efficiency and utilization of such a link, it is necessary for several video signals to share the link. For example, it may be desired to share the above satellite transmission link among at least six video signal channels.